Okay, so I have noticed today that my oil gauge is moving from the center to the bottom then back to the center whenever it is idling in gear, not when it's in Park. No smell that I am aware of at the moment ( I thought ai smelled something a couple of times but I was around cars at those times and haven't noticed a smell when I am alone on the road ), no leaking, or anything else at the moment. Checked the oil, and it looked fine. All this started when I pushed my truck to 70 mph ( never did that since I owned it ). Kept an eye on everything and it seems fine when driving, just when I am idling in traffic. If anyone can give me an idea what it might be it would be very helpful, as I think it's either a clogged filter or the oil sensor or whatever it's called might be going because I think I never changed it.

 

OilLevel on DipStick?
OilWeight?
Miles\Time since last Oil+Filter Change?
Miles on Vehicle+Engine?

Note, your 2001 InstrumentCluster (same on this era Explorer+Ranger+SportTrac+MazdaB+...)
is fitted with a fake OilPressureGage+Needle, as the Engine is FactoryEquipped with only an OilPressureSwitch;
this is only a simple PressureSwitch+Indicator that toggles Off~On at 6~8psi, not a fully variable PressureSensor+Gage;
despite appearance the InstrumentCluster OilPressureNeedle is Off~On only & not a variable Gage.
As the Engine+OilPresureSwitch age, OilSludge+ThreadCorrosion eventually causes this Switch to become erratic.

Things to try to get OilPressureSwitch+Indicator to work better:
* Use slightly thicker OilWeight: for example switch 0w20 to 0w30, or 5w30 to 5w40
* Remove PressureSwitch, clean Switch+OilPassage with CarbCleaner, do not use RTV\TeflonTape on threads as it interfers with circuit
* Renew PressureSwitch
* Remove InstrumentCluster, clean+tighten all Electrical Pins+Connections+Grounds

Click here for more info on this OilPressureSwitch+Indicator.

 

Since the late 1980's Ford has used an Oil Pressure Switch, on/off switch
Its normal pressure rating is 5psi or less = OFF
6psi or more = ON

The switch grounds the Oil Pressure gauge in the cab when its ON, causing the gauge to show in the "normal" range
When there is no ground(OFF) then 0 is displayed on the gauge

So your description means at warm idle your oil pressure is hovering around 5-6psi, causing the on/off for oil pressure gauge
Anything above 4psi at idle is fine, but it is unnerving to see oil pressure drop to 0psi, lol, but on this type of system its not really 0psi, just under 6psi
At 3psi you would start to hear rocker/lifter clatter from the top of the engine, you don't mention that so oil pressure is for sure not dropping below 4psi



Oil pressure is measured in the main oil passage after the oil goes thru the filter
The oil pressure sender/switch is between the filter and the bearings
So oil pressure is BACK PRESSURE, the oil the engine can not use at that time
The gaps in the bearings and other outlets for the oil can only flow X amount of oil thru at any given time, so the oil coming from the pump and filter "backs up" in the main passage, and thats "oil pressure"

As engine RPMs go up the oil pump pumps more oil, but the bearings and oil ports need for more oil doesn't go up as much so the Back Pressure goes up, 10psi, 20psi, 30psi, ect......
General "rule of thumb" is each 1,000rpm = 10psi, so engine at 3,000rpm should have about 30psi oil pressure
Engine at idle at 700rpm = 7psi, so the engine at idle CAN NOT USE the extra 7psi of oil the pump and filter is providing

As an engine gets more miles the bearing gaps will increase from wear, so more oil can pass thru, so at 700rpm idle oil pressure may be 5-6psi and cause the flickering oil gauge
You can change the oil pressure sender/switch, just to take that off the table
You can switch to a 40w oil viscosity which raises oil pressure slightly after warm up, a "high mile oil"

The reason Ford, and most automakers, changed to an oil pressure switch(or oil light) is because of a growing population that didn't understand "oil pressure" in engines
Service departments were getting more and more owners coming in with a "problem" related to oil pressure, there was no problem, 7psi is fine at warm idle, lol
There are other ways to "fudge" low oil pressure gauge limits, i.e. electronics, but the least expensive way is to change to an ON/OFF switch with a preset gauge resistor to show "normal"